Control valve for variable displacement compressor

ABSTRACT

In order to reduce the amount of refrigerant circulating within a variable displacement compressor to thereby improve compression efficiency, a control valve is configured to comprise a ball valve for controlling the flow rate of refrigerant flowing from a discharge chamber to a crankcase, a spool valve for controlling the flow rate of refrigerant flowing from the crankcase to a suction chamber, a diaphragm for sensing suction pressure, and a solenoid for setting the suction pressure, wherein the spool valve starts flow rate control after the ball valve is fully closed or nearly fully closed, and the ball valve starts flow rate control after the valve lift of the spool valve is minimized or nearly minimized. As a result, a region is almost eliminated in which the ball valve and the spool valve are both open simultaneously during switching of flow rate control between the ball valve and the spool valve, which makes it possible to minimize the flow rate of the refrigerant circulating within the compressor without contributing to a refrigerating operation, to thereby improve the efficiency of the compressor.

This application is a continuing application, filed under 35 U.S.C.§111(a), of International Application PCT/JP2004/000505, filed Jan. 21,2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control valve for a variabledisplacement compressor, and more particularly to a control valve for avariable displacement compressor used in a refrigeration cycle of anautomotive air conditioner.

2. Description of the Related Art

The rotational speed of an engine as a drive source of an automotive airconditioner is not constant, and hence the air conditioner is requiredto be controlled such that refrigerating power thereof is held constantregardless of the engine rotational speed. To meet this requirement, aswash plate variable displacement compressor capable of changing thedischarge amount of refrigerant is generally used in an automotive airconditioner. In the variable displacement compressor, a swash platedisposed within a crankcase such that the inclination angle thereof canbe changed is driven by the rotation of a rotating shaft, for performingwobbling motion, and the wobbling motion causes a plurality of pistonsto perform reciprocating motion in a direction parallel to the rotatingshaft, whereby refrigerant is drawn, compressed, and then discharged. Indoing this, the inclination angle of the swash plate is varied bychanging the pressure in the crankcase, whereby the stroke of thepistons is changed for changing the discharge amount of the refrigerant.

In general, the control valve is disposed in a refrigerant passagecommunicating between a discharge chamber and a crankcase, and controlsthe flow rate of refrigerant introduced at discharge pressure Pd fromthe discharge chamber into the crankcase, to thereby control pressure Pcwithin the crankcase. The refrigerant introduced into the crankcase isdrawn into the suction chamber via a fixed orifice. In this controlvalve, suction pressure Ps in the suction chamber is sensed e.g. by apressure-sensing member, such as a diaphragm, and the flow rate of therefrigerant introduced into the crankcase is controlled such that thesuction pressure Ps is maintained at a constant level.

On the other hand, it is also conventional to dispose a control valve ina refrigerant passage communicating between the crankcase and thesuction chamber, and provide a fixed orifice between the dischargechamber and the crankcase, so as to control the flow rate of therefrigerant drawn from the crankcase.

In either of the variable displacement compressors using these two typesof control valves, the fixed orifice having an invariable flow passagearea is interposed in the passage from the discharge chamber to thecrankcase or the passage from the crankcase to the suction chamber inseries with the passage. Consequently, in the variable displacementcompressor using one of the above-described control valves, increasedamount of refrigerant circulates therein, which inevitably causesdegradation of compression efficiency.

There has also been proposed a control valve having two valves disposed,respectively, in the refrigerant passage communicating between thedischarge chamber and the crankcase and the refrigerant passagecommunicating between the crankcase and the suction chamber, such thatthe two valves operate in a manner interlocked with each other, so as tosimultaneously control the flow rate of the refrigerant introduced intothe crankcase and the flow rate of the refrigerant drawn from thecrankcase (e.g. in Japanese Unexamined Patent Publication (Kokai) NO.S58-158382, FIG. 3). With this configuration, the control valve providescontrol such that when the flow rate of refrigerant in one of therefrigerant passage communicating between the discharge chamber and thecrankcase and the refrigerant passage communicating between thecrankcase and the suction chamber is increased, the flow rate ofrefrigerant in the other is reduced. This makes it possible to reducethe flow rate of refrigerant circulating in the variable displacementcompressor, and hence construct a variable displacement compressor whichis higher in compression efficiency than those using the control valvesconfigured as described hereinbefore.

Further, there has been proposed a control valve having two valvesdisposed, respectively, in the refrigerant passage communicating betweenthe discharge chamber and the crankcase and the refrigerant passagecommunicating between the crankcase and the suction chamber, such thatthe two valves operate in a manner interlocked with each other to holdone of the refrigerant passages in a closed state when the other passageis open in a controlled state (e.g. in Japanese Unexamined PatentPublication (Kokai) No. S64-41680, FIG. 2). According to this controlvalve, when the flow rate of refrigerant in one of the refrigerantpassages is being controlled, the other refrigerant passage is closed,so that refrigerant circulating in the variable displacement compressorcan be further reduced.

However, in the former control valve described in Japanese UnexaminedPatent Publication (Kokai) No. S58-158382, in which the valves aredisposed on the respective inlet and outlet sides of the crankcase, oneof the two valves operated in an interlocked manner closes as the otheropens, and hence there inevitably occurs a region where the two valvesare both open. Consequently, the flow rate of refrigerant circulating inthe compressor can only be reduced to a limited degree, which makes itimpossible to obtain sufficiently improved compression efficiency.

On the other hand, in the latter control valve described in JapaneseUnexamined Patent Publication (Kokai) No. S64-41680, in which while oneof the valves is open, the other is held closed, when the suctionpressure becomes not higher than a first set pressure, the refrigerantpassage (outlet side) between the crankcase and the suction chamber isfully closed, and hence the pressure in the crankcase sensitively reactsto a slight change in the valve in the refrigerant passage (inlet side)between the discharge chamber and the crankcase. As a consequence, whenthe pressure in the crankcase rises excessively, gaseous refrigerantcompressed in the crankcase cannot be reduced by changing the valve liftof the valve on the inlet side, and not until the suction pressurespontaneously becomes higher than a second set pressure with decrease inthe displacement of the compressor to open the outlet-side refrigerantpassage, does the pressure in the crankcase fall. Then, the displacementof the compressor increases with decrease in the pressure in thecrankcase, and the suction pressure becomes not higher than the firstset pressure. Thereafter, a so-called hunting phenomenon occurs in whichthe above-described cycle is repeated. As described above, the lattercontrol valve cannot ensure stable controllability.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above points, and anobject thereof is to provide a control valve for a variable displacementcompressor, which is capable of reducing the amount of refrigerantcirculating within the compressor to thereby improve compressionefficiency, while ensuring stable controllability.

To solve the above problems, the present invention provides a controlvalve for a variable displacement compressor, which is capable ofcontrolling pressure in a crankcase to thereby change a discharge amountof refrigerant, comprising a first valve that is disposed between adischarge chamber and the crankcase of the compressor, for controlling aflow rate of refrigerant flowing from the discharge chamber to thecrankcase, a second valve that is disposed between the crankcase and asuction chamber of the compressor, for controlling a flow rate ofrefrigerant flowing from the crankcase to the suction chamber to apredetermined minimum rate when the first valve is controlling the flowrate of the refrigerant flowing from the discharge chamber to thecrankcase, and for controlling the flow rate of the refrigerant flowingfrom the crankcase to the suction chamber when the first valve is fullyclosed or nearly fully closed, and a pressure-sensing section thatsenses suction pressure in the suction chamber, for changing a liftamount of the first valve and a lift amount of the second valve.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view showing the arrangement of a control valvefor a variable displacement compressor, according to the presentinvention.

FIG. 2 is an enlarged fragmentary view useful in explaining the controlvalve set to a first opening/closing timing.

FIG. 3 is a diagram showing characteristics of the control valve set tothe first opening/closing timing.

FIG. 4 is an enlarged fragmentary view useful in explaining the controlvalve set to a second opening/closing timing.

FIG. 5 is a diagram showing characteristics of the control valve set tothe second opening/closing timing.

FIG. 6 is an enlarged fragmentary view useful in explaining the controlvalve set to a third opening/closing timing.

FIG. 7 is a diagram showing characteristics of the control valve set tothe third opening/closing timing.

FIG. 8 is an enlarged fragmentary view useful in explaining a controlvalve in which a fixed orifice is formed in each of an inlet side and anoutlet side.

FIG. 9 is a diagram showing characteristics of the control valve set toa fourth opening/closing timing.

FIG. 10 is a conceptual view showing a control valve in which a fixedorifice is formed in each of an inlet side and an outlet side.

FIG. 11 is a diagram showing characteristics of the control valve set toa fifth opening/closing timing.

FIG. 12 is a conceptual view showing the arrangement of a mechanicalcontrol valve for a variable displacement compressor.

FIG. 13 is a conceptual view showing the arrangement of a mechanicalcontrol valve for a variable displacement compressor.

FIG. 14 is a conceptual view showing the arrangement of a control valvefor a variable displacement compressor, in which the fixed orificefunction of a second valve is provided independently.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe accompanying drawings showing preferred embodiments thereof.

FIG. 1 is a conceptual view showing the arrangement of a control valvefor a variable displacement compressor, according to the presentinvention.

The control valve for a variable displacement compressor, according tothe present invention has a ball valve 11 forming a first valve, a spoolvalve 12 forming a second valve, a diaphragm 13 forming apressure-sensing section, and a solenoid 14 forming a pressure-settingsection, which are arranged in the mentioned order.

The ball valve 11 introduces refrigerant discharged at dischargepressure Pd from a discharge chamber of the variable displacementcompressor, and controls the flow rate of the introduced refrigerant tosupply the refrigerant at pressure Pc1 to a crankcase. The spool valve12 introduces refrigerant delivered at pressure Pc2 from the crankcase,and controls the flow rate of the introduced refrigerant to supply thepressure to a suction chamber of the compressor in a manner interlockedwith operation of the ball valve 11. The diaphragm 13 receives suctionpressure Ps from the suction chamber, and when the suction pressurebecomes lower than a predetermined suction pressure setting point, thediaphragm 13 displaces the ball valve 11 and the spool valve 12 toincrease pressure in the crankcase. With increase in the pressure in thecrankcase, the displacement of the compressor is reduced. As aconsequence, the suction pressure of an air conditioner is controlled toa level in the vicinity of the predetermined suction pressure settingpoint. The solenoid 14 applies urging load to the diaphragm 13 to setthe suction pressure setting point. The urging load is set according tothe value of an electric current externally supplied.

The spool valve 12 comprises a valve seat 15 and a valve element 16removably inserted into a valve hole. Between the valve seat 15 and thevalve element 16, there is formed a predetermined clearance 17. Thisclearance 17 forms a fixed orifice with an invariable flow passage areabetween the crankcase and the suction chamber when the valve element 16is inserted into the valve hole. The clearance 17 is determineddepending on the stability of the swash plate of the compressor. Thevalve element 16 is integrally formed with a shaft 18 for driving theball valve 11. The valve element 16 and the shaft 18 are joined to eachother by a joining part 19 having a frustoconical shape with a taper incross section.

The spool valve 12 can be freely modified according to characteristics,such as hunting, controllability, and stability, of the variabledisplacement compressor such that the spool valve 12 has a differentopening/closing timing from that of the ball valve 11 interlocking withoperation of the spool valve 12. The change in the opening/closingtiming of the spool valve 12 can be easily achieved by changing thedistance between an end of the valve element 16 as a boundary to thejoining part 19 and a forward end of the shaft 18 in contact with avalve element 20 of the ball valve 11 to thereby axially shift aposition where the end of the valve element 16 is held in a fully-closedstate of the ball valve 11.

In the ball valve 11, as the shaft 18 moves rightward as viewed in FIG.1, the valve element 20 moves in a valve-opening direction, and themaximum valve lift of the ball valve 11 is limited by abutment of astepped part 21 of the shaft 18 against a stepped part 22 of a body.

FIG. 2 is an enlarged fragmentary view useful in explaining the controlvalve set to a first opening/closing timing, and FIG. 3 is a diagramshowing characteristics of the control valve set to the firstopening/closing timing.

The first opening/closing timing is set such that the opening/closingtiming of the ball valve 11 and that of the spool valve 12 coincide witheach other, and more specifically such that when the ball valve 11 isfully closed, the end of the valve element 16 of the spool valve 12 isaligned with a solenoid-side open end face of the valve seat 15.

With this configuration, the characteristics exhibited by the controlvalve when the valve element 16 of the spool valve 12 is axially movedare as shown in FIG. 3. In FIG. 3, the abscissa represents a stroke ofthe shaft 18, and the origin represents a state where the stepped part21 of the shaft 18 is in abutment with the stepped part 22 of the bodyand at a position closest to the ball valve side (or a deenergized stateof the solenoid). The ordinate in FIG. 3 represents the opening area ofthe ball valve 11 and that of the spool valve 12. A line indicated byPd-Pc represents changes in the opening area of the ball valve 11, whilea line indicated by Pc-Ps represents changes in the opening area of thespool valve 12.

In the first opening/closing timing, as long as the ball valve 11 isopen, the spool valve 12 has an opening area corresponding to theclearance 17, and operates as the fixed orifice. When the shaft 18 movestoward the solenoid 14 and reaches a position s1, the valve element 20of the ball valve 11 is seated to fully close the ball valve 11. Whenthe shaft 18 further moves toward the solenoid 14, the forward end ofthe shaft 18 moves away from the valve element 20 of the ball valve 11,whereby the ball valve 11 is held in its fully-closed state, and thespool valve 12 starts opening from the state operating as the fixedorifice to increase its opening area in accordance with increase in thestroke of the shaft 18. When the ball valve 11 is in its fully-closedstate, compressed refrigerant cannot flow into the crankcase via thecontrol valve, but a slight amount of blowby gas leaks into thecrankcase through a gap between a piston for drawing and compressingrefrigerant and a cylinder having the piston slidably received therein,which makes it possible to control pressure Pc (=Pc1=Pc2) within thecrankcase.

FIG. 4 is an enlarged fragmentary view useful in explaining the controlvalve set to a second opening/closing timing, and FIG. 5 is a diagramshowing characteristics of the control valve set to the secondopening/closing timing.

The second opening/closing timing is set such that the opening timing ofthe spool valve 12 is retarded with respect to the closing timing of theball valve 11, and hence in the second opening/closing timing, when theball valve 11 is fully closed, the spool valve 12 is still in its closedstate (fixed orifice state). To this end, the distance between the ballvalve-side end of the valve element 16 and the forward end of the shaftin contact with the valve element 20 of the ball valve 11 is madeshorter by a distance “a” than in the first opening/closing timing suchthat when the ball valve 11 is closed, the ball valve-side end of thevalve element 16 of the spool valve 12 is positioned within the valvehole.

With this configuration, in the second opening/closing timing, as shownin FIG. 5, as the shaft 18 moves toward the solenoid 14, first, the ballvalve 11 is fully closed when the shaft 18 reaches the position s1. Atthis time, the spool valve 12 has the opening area corresponding to theclearance 17. Then, when the shaft 18 further moves toward the solenoid14 and reaches a position s2, the spool valve 12 starts opening.

FIG. 6 is an enlarged fragmentary view useful in explaining the controlvalve set to a third opening/closing timing, and FIG. 7 is a diagramshowing characteristics of the control valve set to the thirdopening/closing timing.

The third opening/closing timing is configured such that the openingtiming of the spool valve 12 is advanced with respect to the closingtiming of the ball valve 11. To this end, the distance between the ballvalve-side end of the valve element 16 and the forward end of the shaftin contact with the valve element 20 of the ball valve 11 is made longerby a distance “b” than in the first opening/closing timing whereby whenthe ball valve 11 is closed, the ball valve-side end of the valveelement 16 of the spool valve 12 is positioned closer to the solenoid 14than the valve seat 15.

With this configuration, in the third opening/closing timing, as shownin FIG. 7, as the shaft 18 moves toward the solenoid 14, first, thespool valve 12 starts opening when the shaft 18 reaches a position s1,and then when the shaft 18 reaches a position s2, the ball valve 11 isfully closed.

FIG. 8 is an enlarged fragmentary view useful in explaining a controlvalve in which a fixed orifice is formed in each of an inlet side and anoutlet side, and FIG. 9 is a diagram showing characteristics of thecontrol valve set to a fourth opening/closing timing. It should be notedthat component elements in FIG. 8 identical to those in FIG. 1 aredesignated by identical reference numerals.

This control valve is configured such that the fixed orifices are formedon the respective inlet and outlet sides of the crankcase. In thecontrol valve, the forward end of the shaft 18 in contact with the valveelement 20 of the ball valve 11 is formed into a spool shape, and aclearance 24 is formed between the outer periphery of a contact end part23 of the shaft 18 and the inner wall of the valve hole. When the ballvalve 11 is in the vicinity of its fully-closed position, the clearance24 is formed within the valve hole to form a fixed orifice with aninvariable flow passage area between a compression chamber and thecrankcase. The fixed orifice is provided for stably maintaining the flowrate of refrigerant introduced from the discharge chamber into thecrankcase in a region where refrigerant is introduced into the crankcaseby blowby gas, and the flow rate of refrigerant discharged from thecrankcase is controlled by the spool valve 12. The distance between therear end (diameter reduction start position) of the contact end part 23and the seated position of the valve element 20 is set to a distance“c”. Further, in the present example, the distance “d” between the endof the valve element 16 of the spool valve 12 and a valve closing startposition of the spool valve 12 is set such that it becomes equal invalue to the distance “c” when the ball valve 11 is fully closed withthe valve element 20 thereof held in contact with the contact end part23.

The control valve set as above has the following characteristics: Asshown in FIG. 9, first, when the solenoid is not energized, the steppedpart 21 of the shaft 18 is in contact with the stepped part 22 of thebody, and hence the ball valve 11 is in its fully-open state, and thespool valve 12 is in the fixed orifice state.

With an increase in electric current for energizing the solenoid, theball valve 11 turns from the fully-open state in the direction ofreducing its opening area, whereas the spool valve 12 maintains itsfixed orifice state. Then, when the shaft moves to a position s1, therear end of the contact end part 23 reaches the seated position of thevalve element 20, and the spool valve 12 reaches a valve opening startposition at which it starts to get out of the fixed orifice state. Whenthe shaft 18 further moves from the position s1, the rear end of thecontact end part 23 enters the valve hole, whereby the ball valve 11enters its fixed orifice state, and the spool valve 12 changes from itsfixed orifice state in the direction of increasing its opening area.

Thereafter, the fixed orifice state of the ball valve 11 is maintaineduntil the opening area of the ball valve 11 becomes smaller than that ofthe fixed orifice, and finally the ball valve 11 is seated to be fullyclosed.

Although in the above example, the distance “c” and the distance “d” areset to the same value, the distance “d” may be increased or decreasedaccording to the characteristics of the variable displacement compressorto thereby easily change the opening/closing timing of the spool valve12.

FIG. 10 is a conceptual view showing the arrangement of a control valvein which a fixed orifice is formed in each of the inlet side and theoutlet side, and FIG. 11 is a diagram showing characteristics of thecontrol valve set to a fifth opening/closing timing. It should be notedthat component elements in FIG. 10 identical to those in FIG. 1 aredesignated by identical reference numerals.

In this control valve, a valve disposed between the compressor and thecrankcase and a valve disposed between the crankcase and the suctionchamber are implemented by respective spool valves 11 a and 12. Thevalve element 16 of the spool valve 12, the shaft 18, and a valveelement 20 a of the spool valve 11 a are integrally formed with eachother. The valve element 20 a is smaller in diameter than the shaft 18supported by the body, and the clearance 24 is formed between the valveelement 20 a and the inner wall of the valve hole. Further, a portionbetween the valve element 20 a and the shaft 18 is reduced in diameterto have a spool shape. The distance between the rear end (diameterreduction start position) of the valve element 20 a and a valve closingstart position where the valve element 20 a enters the valve hole is setsuch that it becomes equal to a distance “e” when the spool valve 12 isin a valve closing start position.

The control valve set as above has the following characteristics: Asshown in FIG. 11, first, when the solenoid is not energized, the steppedpart 21 of the shaft 18 is in contact with the stepped part 22 of thebody, and hence the spool valve 11 a is in its fully-open state, and thespool valve 12 is fully closed and in its fixed orifice state.

With an increase in electric current for energizing the solenoid, therear end of the valve element 20 a of the spool valve 11 a approachesthe valve hole and changes from its fully-open state in the direction ofreducing its opening area, whereas the spool valve 12 maintains itsfixed orifice state. Then, when the shaft 18 moves to a position s1, thespool valve 11 a reaches the valve closing start position, and the spoolvalve 12 reaches a valve opening start position at which it starts toget out of its fixed orifice state. When the shaft 18 further moves fromthe position s1, the valve element 20 a enters the valve hole, wherebythe spool valve 11 a enters its fixed orifice state, and the spool valve12 changes from its fixed orifice state in the direction of increasingits opening area.

In the above embodiments, the electric control valves are describedwhich use, as means for setting the suction pressure Ps in the suctionchamber, the solenoid that enables a set point (pressure control point)thereof to be freely set by external electric control current. Next,mechanical control valves will be describe in which the suction pressurePs is set to a fixed value.

FIG. 12 is a conceptual view showing the arrangement of a mechanicalcontrol valve for a variable displacement compressor. It should be notedthat component elements in FIG. 12 identical to those in FIG. 1 aredesignated by identical reference numerals, and detailed descriptionthereof is omitted.

This control valve has the ball valve 11 forming the first valve, thespool valve 12 forming the second valve, the diaphragm 13 forming thepressure-sensing section, and a spring 25 forming a pressure-settingsection, which are arranged in the mentioned order.

This control valve is also configured such that as long as the ballvalve 11 is variably controlling its opening area, the spool valve 12functions as a fixed orifice, and when the ball valve 11 is in itsfully-closed state, the spool valve 12 variably controls its openingarea. Of course, the opening/closing timing of the spool valve 12 is setto one of the above described first to third opening/closing timings inaccordance with the characteristics of the variable displacementcompressor.

The diaphragm 13 has a disk 26 provided on a spring-side surfacethereof, and the spring 25 urges the diaphragm 13 toward the spool valve12 via the disk 26. The spring 25 is adjusted to have a spring loadcorresponding to a predetermined suction pressure control point.Therefore, when the suction pressure Ps received from the suctionchamber becomes lower than the suction pressure control point, thediaphragm 13 urges the ball valve 11 and the spool valve 12 such thatthe pressure in the crankcase is increased, whereby the control valvecontrols the displacement of the variable displacement compressor tothereby control suction pressure in the air conditioner to a level inthe vicinity of the predetermined suction pressure control point.

Of course, the present control valve can also be configured as a controlvalve set to the fourth opening/closing timing, by forming the contactend part 23 at the end of the shaft 18 to form the fixed orifice shownin FIG. 8 and thereby forming the fixed orifices on the respectiverefrigerant inlet and outlet sides of the crankcase.

FIG. 13 is a conceptual view showing the arrangement of a mechanicalcontrol valve for a variable displacement compressor. It should be notedthat component elements in FIG. 13 identical to those in FIGS. 1 and 10are designated by identical reference numerals, and detailed descriptionthereof is omitted.

This control valve has the spool valve 11 a forming the first valve, thespool valve 12 forming the second valve, the diaphragm 13 forming thepressure-sensing section, and the spring 25 forming the pressure-settingsection, which are arranged in the mentioned order.

The spool valve 11 a is identical in construction to that shown in FIG.10. Therefore, the present control valve has the characteristic of thefifth opening/closing timing shown in FIG. 11.

Also in this control valve, the suction pressure Ps is received from thesuction chamber to change the lift amount of each of the spool valves 11a and 12, and the pressure in the crankcase is controlled such that thesuction pressure Ps is held constant as a consequence.

FIG. 14 is a conceptual view showing the arrangement of a control valvefor a variable displacement compressor, in which the fixed orificefunction of the second valve is provided independently. It should benoted that component elements in FIG. 14 identical to those in FIG. 1are designated by identical reference numerals, and detailed descriptionthereof is omitted.

The present control valve is distinguished from the control valve shownin FIG. 1, in which the clearance 17 formed between the valve element 16of the spool valve 12 and the inner wall of the valve hole provides thefixed orifice function, in that a fixed orifice 27 having an openingarea equivalent to that formed by the clearance 17 is formed in thebody. In this case, the clearance 17 formed between the valve element 16of the spool valve 12 and the inner wall of the valve hole is minimized.As a result, when the refrigerant passage between the crankcase and thesuction chamber is narrowed by the spool valve 12, refrigerant is causedto flow through the fixed orifice 27 larger in diameter, and preventedfrom flowing through the clearance 17 which is small. This provides anadvantageous effect that a change in the flow rate of refrigerant due todeposition of sludge contained in the refrigerant can be reduced.

More specifically, assuming that the clearance 17 between the valveelement 16 of the spool valve 12 and the inner wall of the valve hole ise.g. 0.1 mm, the fixed orifice 27 having an opening area equivalent tothe clearance 17 is a through hole with a diameter of 1 mm, and sludgedeposited on the valve element 16 or the inner wall of the valve hole,or on the inner wall of the fixed orifice 27 has grown e.g. to athickness of 0.1 mm, the clearance 17 is almost clogged with the sludge,whereas the diameter of the fixed orifice 27 is reduced only to 0.8 mm,which makes smaller the change in the flow rate of refrigerant due todeposition of sludge. Further, since refrigerant mainly flows throughthe fixed orifice 27 which is easier for refrigerant to flow through,the amount of refrigerant flowing through the narrow clearance 17 issmall, which makes it difficult for sludge to deposit.

Although the arrangement in which the fixed orifice 27 is formed inparallel with the spool valve 12 forming the second valve is describedbased on an example of application thereof to the control valve of atype having the solenoid 14 shown in FIG. 1, it can also be applied tothe mechanical control valves shown in FIGS. 12 and 13.

As described above, according to the present invention, the controlvalve is configured to comprise the first valve for controlling the flowrate of refrigerant flowing from the discharge chamber to the crankcase,the second valve for controlling the flow rate of refrigerant flowingfrom the crankcase to the suction chamber, the pressure-sensing sectionfor sensing suction pressure, and the pressure-setting section forsetting the suction pressure, wherein the second valve starts flow ratecontrol after the first valve is fully closed or nearly fully closed,and the first valve starts flow rate control after the valve lift of thesecond valve is minimum or nearly minimum. As a result, a region iseliminated in which the first and second valves are both opensimultaneously during switching of control between the first valve andthe second valve, which makes it possible to minimize the flow rate ofrefrigerant flowing from the discharge chamber to the crankcase andfurther from the crankcase to the suction chamber, i.e. the flow rate ofrefrigerant circulating within the variable displacement compressorwithout contributing to a refrigerating operation, to thereby improvethe efficiency of the compressor. Further, since the second valve isequipped with the fixed orifice function for reducing the flow rate ofrefrigerant flowing from the crankcase to the suction chamber to apredetermined minimum flow rate, it is possible to stably adjust thepressure in the crankcase to thereby provide excellent controllability.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A control valve for a variable displacement compressor, which iscapable of controlling pressure in a crankcase to thereby change adischarge amount of refrigerant, comprising: a first valve that isdisposed between a discharge chamber and the crankcase of thecompressor, for controlling a flow rate of refrigerant flowing from thedischarge chamber to the crankcase; a second valve that is disposedbetween the crankcase and a suction chamber of the compressor, forcontrolling a flow rate of refrigerant flowing from the crankcase to thesuction chamber to a predetermined minimum rate when the first valve iscontrolling the flow rate of the refrigerant flowing from the dischargechamber to the crankcase, and for controlling the flow rate of therefrigerant flowing from the crankcase to the suction chamber when thefirst valve is fully closed or nearly fully closed; and apressure-sensing section that senses suction pressure in the suctionchamber, for changing a lift amount of the first valve and a lift amountof the second valve.
 2. The control valve according to claim 1, whereinthe second valve has a clearance set between a diameter of a valve holeand a diameter of a valve element inserted into the valve hole when thefirst valve is controlling the flow rate of the refrigerant flowing fromthe discharge chamber to the crankcase, the clearance being providedwith a fixed orifice function for controlling the flow rate of therefrigerant flowing from the crankcase to the suction chamber to thepredetermined minimum rate.
 3. The control valve according to claim 1,comprising a shaft extending through the valve hole of the second valvecoaxially with the valve hole, for transmitting an opening/closingoperation of the second valve to the first valve.
 4. The control valveaccording to claim 3, wherein the shaft has a joining part joined to thevalve element, formed such that the joining part has a frustconicalshape.
 5. The control valve according to claim 3, wherein the shaft hasan end thereof in contact with a valve element of the first valve,formed such that the end has a spool shape.
 6. The control valveaccording to claim 3, wherein the shaft can be brought into contact withand left the valve element of the first valve.
 7. The control valveaccording to claim 3, wherein a clearance set between a diameter of anend of the shaft in contact with the valve element of the first valveand a diameter of a valve hole of the first valve is provided with afixed orifice function for controlling the flow rate of the refrigerantflowing from the discharge chamber to the crankcase to the predeterminedminimum rate.
 8. The control valve according to claim 1, wherein thefirst valve is a spool valve.
 9. The control valve according to claim 1,comprising a fixed orifice that is formed in parallel with the secondvalve, for controlling the flow rate of the refrigerant flowing from thecrankcase to the suction chamber to the predetermined minimum rate whenthe first valve is controlling the flow rate of the refrigerant flowingfrom the discharge chamber to the crankcase.
 10. The control valveaccording to claim 1, comprising a pressure-setting section that appliesurging load to the pressure-sensing section to set a pressure controlpoint of the control valve.
 11. The control valve according to claim 10,wherein the pressure-setting section is a solenoid that sets thepressure control point by applying the urging load in response to anexternal signal.
 12. The control valve according to claim 10, whereinthe pressure-setting section is a spring that sets the pressure controlpoint by a spring force.